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It is commonly said that eating slower will reduce your appetite. This site, for example, claims:

Portion control & Overeating prevention. When you eat slowly it is definitely hard to overeat. Slow eating little by little decreases the desire to eat, so you can stop eating before your plate is empty. It is suggested that it takes about 20 minutes for your stomach to produce the hormones telling your brain that you are full.

Weight control benefits. Slowly eating habit reduces the risk of becoming overweight. Recently Japanese researches found strong positive correlation between higher eating speed and obesity.

Is it true that eating a meal more slowly will make one prefer to eat less? Could this help to lose weight?

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    I think the claim is that eating slower makes you eat less, not that it makes you lose weight. In other words, nobody is claiming that if you eat salad fast and substitute with eating chocolate slowly, then you'll lose weight. Please update the question so it's clear what variables we are keeping fixed, etc. – Sklivvz Jul 2 '11 at 7:56
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    Thanks for the clarification, @picakhu. I have substantially edited the question based on it. Please check I am still capturing your question. – Oddthinking Jul 2 '11 at 9:41
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    I think its because when you eat slower, you tend to chew the food more, making the pieces smaller and more digestible. – Thursagen Jul 2 '11 at 13:30
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    @Martin, @Ham: I say this without any great knowledge of the workings of the digestive system, but wouldn't your theory run counter to weight gain? If smaller bits of food are somehow digested more completely as you suggest, wouldn't that mean that your body is actually absorbing more? Wouldn't it follow that with more absorption comes more weight gain? If you're not digesting properly, food is just going to go right through you; you can't gain weight from undigested food. – erekalper Jul 6 '11 at 15:51
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    The basis for this is the fact that there is a time lag due to appetite and the sensation of being full being communicated through the endocrine system (secreting hormones and chemicals vs. just nerve impulses). If you are very hungry, and eat fast, you will still have the sensation of being hungry even when you are full because of that time lag in relaying the "I'm full" message through the system. Slowing down prevents the amount of food from getting too far ahead of the body's messaging. – PoloHoleSet Sep 22 '16 at 16:29
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The Japanese research indicated is available here in the BMJ. It is based on a survey of >3000 people's self reported eating habits in a Japanese village.

it does show a very strong correlation between people indicating they "eat quickly" or who "eat until they are full" and incidence of obesity.

The BMJ itself wrote that participants were according to this report

The researchers also found that both men and women in the "eating until full and eating quickly" were three times more likely to be overweight than the participants from the "not eating until full and not eating quickly" group.

Now obviously correlation is not causation, but it is at the least an indicator that changing your eating habits to take more time can mean less energy intake at mealtimes.

Whether this will lead to one losing weight long term is obviously dependent on a whole host of other factors.

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No, because overweight is a metabolic issue and not a behavioral one.

It's currently the fashion to believe that overweight people suffer from sloth and gluttony; however, adipose tissue is not the result of character defects but rather of metabolic function. As it turns out, the obese don't consume more calories than the lean.

“Most studies comparing normal and overweight people suggest that those who are overweight eat fewer calories than those of normal weight.” [National Academy of Sciences, Diet and Health]

Not all calories are created equal. The body metabolizes them differently. The current belief is that:

A calorie of protein provides the same amount of energy to the body as a calorie of fat or carbohydrate. Lost in this distillation is the fact that the effects of these different nutrients on metabolism and hormone secretion are so radically different, as is the manner in which the body employs the nutrients, that the energetic equivalence of the calories themselves is largely irrelevant to why we gain weight. As Rubner suggested more than a century ago, “the effect of specific nutritional substances upon the glands” may be the more relevant factor. [Taubes, Gary (2007). Good Calories, Bad Calories (p. 276). Anchor.]

Insulin regulates body fat. Modern diets are full of refined carbohydrates that cause excessively high blood glucose, and this in turn causes the pancreas to secrete insulin to force the tissues store it as fat.

To lose fat, keep the blood sugar under control by avoiding refined carbohydrates like white sugar, white flour, potatoes, beer, and white rice. You don't need to force yourself to eat slowly. (The research doesn't yet exist for me toI can't prove this assertion, but here is a great list of the current state of research.)

The current wisdom is that to lose weight, one must eat less and exercise more (as if the human body were a car, and all food was petrol), and yet anyone who has ever tried this approach knows it's uncomfortable at best. However, it's beginning to appear that changing the types of calories we consume rather than the quantity is actually more appropriate:

We're beginning to see meta studies as well:

An even more recent meta-study of randomized controlled studies that compared low-carbohydrate diets to low-fat/low-calorie diets found that measurements of weight, HDL cholesterol, triglyceride levels and systolic blood pressure were significantly better in groups that followed low-carbohydrate diets. The authors also found a higher rate of attrition in groups with low-fat diets. They conclude that "Evidence from this systematic review demonstrates that low-carbohydrate/high-protein diets are more effective at 6 months and are as effective, if not more, as low-fat diets in reducing weight and cardiovascular disease risk up to 1 year."

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    This makes a large number of claims that appear to conflict with the consensus view of nutrition. That doesn't mean it is wrong, but it does mean it needs some substantive evidence to support it. Quotes from a couple of individual nutritionists, in a field known to reward mavericks, doesn't cut it, I am afraid. – Oddthinking Jul 18 '11 at 2:49
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    “It is scientifically well known that the obese do not consume more calories than the lean” – this is at least partially wrong, if not totally. Please find a scientific reference for a tempered version of this claim. The same counts for ret of the claims. – Konrad Rudolph Jul 18 '11 at 12:26
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    Thank you. I've edited it to add references; I hope I've done better. – goblinbox Jul 18 '11 at 20:59
  • Much better. – Konrad Rudolph Jul 19 '11 at 9:13
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    "No, because overweight is a metabolic issue and not a behavioral one." Those are not mutually exclusive. – Muhd Dec 21 '12 at 1:14
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The mechanism behind the "eating slower" claim is because of hunger. Whether one is hungry or satiated/full is communicated through the endocrine system, not directly through signals in the nervous system.

There is a lag time between when the body hormonally signals the stomach is "full" and when that message reaches the brain. In that intervening lag, your brain still feels that you are hungry and you will continue to eat.

If you eat fast, the gap between how full your stomach is and how full your brain thinks the stomach is will be greater. Slowing down allows the hormonal messages sent to the brain to be closer to the real-time, actual situation.

You will feel "full" more accurately, and will not continue to have the urge to keep eating. So, yes, it is true that eating slower will lead to eating less or not over-eating, which obviously impacts weight gain or loss.

Although we can feel the stomach filling up as we eat, it can take 15 - 20 minutes after food is first eaten for the full range of satiety signals to reach the brain. By this time, and for some time afterwards we will experience feelings of fullness (Nutrition.org uk site)

Skeptics StackExchange: Does it take time for your brain to realize you have eaten too much?

When they were asked to eat quickly, they consumed 646 calories in nine minutes. But when they were promoted to slow down and chew the food 15 to 20 times, their calorie consumption was about 579 calories in 29 minutes.

"Satiety signals clearly need time to develop..."

Science Confirms Diet Tactic: Eat Slow, Eat Less

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